Area Forecast Discussion
Issued by NWS Upton, NY

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821 FXUS61 KOKX 161821 AFDOKX Area Forecast Discussion National Weather Service New York NY 121 PM EST Fri Feb 16 2018 .SYNOPSIS... A cold front passes through this afternoon. High pressure builds in tonight through Saturday morning and then passes to the east by afternoon. A coastal low tracks from near the Mid- Atlantic coast Saturday evening to a position southeast of Cape Cod by Sunday morning. High pressure then builds off the eastern seaboard early next week. A cold front then slowly approaches from the west for the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Some minor adjustments were again made to temperatures, dewpoints, and POPs for light rain. Temperatures, especially along the coast, are a little warmer than previously forecast. After a lull in the rain, another batch of light rain behind cold front will be set to move in mid to late this afternoon. Conditions then start to dry out for the interior parts of the region into this evening as the jet passes to the east and a gusty NW flow develops. It will remain cloudy to mostly cloudy through the afternoon. Temperatures remain unseasonably warm with highs between 50 to 60. Temperatures will start to decrease late this afternoon with colder air advecting in on NW flow. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Any lingering light rain exits coastal locations early this evening with clearing skies and a return to seasonable temperatures. Lows will drop down into the 20s most locations and around 30 for the the NYC metro. Strong cold advection this evening will be accompanied by gusty NW winds (up to 30 mph near the coast). Winds diminish fairly quickly toward midnight as high pressure builds in from the west and across the area Saturday morning. The progressive nature of the upper flow, which has been the case for several weeks now, will send the high offshore by afternoon with a weak return flow developing from the SE. An amplifying shortwave trough over the Midwest approaches on Saturday with secondary low development near the Mid Atlantic coast in the afternoon. Any increase in clouds will be late in the day as high temperatures will be a few degrees below normal, in the upper 30s to around 40. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Attention focused on a potent northern stream shortwave diving southeast from near the Alaska coast starting this morning, reaching the Lower Great Lakes/Midwest by Saturday evening, and lifting to near the New England coast by Sunday morning. The GFS seems to have its usual progressive bias with the ridging/damming high ahead of this system, so have opted to go with a non-GFS solution, leaning towards a blend of the NAM/ECMWF/UKMET/SREF. This shortwave will help develop a coastal low along the mid- Atlantic coast Saturday evening, that tracks northeast to a position southeast of Cape Cod by Sunday morning as it deepens. This track takes the storm to the south/east of the 40N/70W bench mark. Given the expected track, and rate of deepening, and with an assist from the isallobaric component of the wind, that winds will quickly go from SE to E to NE as the precipitation begins. This will limit the amount of mixing with rain along the S shore of Long Island during the start of precipitation Saturday evening, with the transition to all snow last over the S Fork of Long Island. Given that it appears that this change over will occur before the heaviest precipitation arrives (except maybe along the S Fork of Long Island by an hour or so), there is the potential for a significant impact across most of the Tri-State. The other limiting factors are QPF, which will be the least over NW portions of the Tri- State, and the relatively quick movement of the storm. There is the potential though for a quick hit of heavy precipitation in banding to the NW of the storm - with some indications that band could extend from NE NJ into SW CT. However, this band could end up father NW or SE than progged. Based on the above, in collaboration with WPC and surrounding offices have issued a Winter Storm Watch from 00z-12Z Sunday for all but Orange and Putnam Counties, and for the potential for 4-7 inches of snow. Orange and Putnam Counties were excluded, because it is more likely than not that there will not be sufficient QPF there to have warning level snowfall. Elsewhere, confidence is at 50 percent for warning level snowfall with uncertainty due to QPF amount, banding placement, and along the S shore of Long Island how quickly any mix with rain changes to all snow. As with any watch, there is the potential for it to be converted to a warning (about 50 percent of the time), or converted to an advisory or cancelled (the other roughly 50 percent of the time). A persistent SW flow then sets up aloft from Sunday into the middle of next week as the region is on the periphery of a closed ridge off the SE coast. This will result in a significant warmup through the middle of next week. Highs Tuesday and Wednesday may get to around 60 across parts of NYC and the interior, but it will be considerably cooler along the coast due an onshore flow. A backdoor cold front passes late Wednesday or Wednesday night, with some cooling expected by Thursday, albeit still above normal. In terms of sensible weather, shortwaves embedded in the SW flow aloft could bring some rain from Monday into Monday night, and then again Wednesday into Wednesday night in conjunction with the aforementioned back door cold front. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... A cold front moves through this afternoon. Mainly VFR, but a period of at least tempo MVFR conds, mainly in cigs, from approx 19-23z. -shra this aftn probably doesn`t cause significant vsby restrictions. W winds at the start quickly shift NW with gusts up to around 25 kt. Gusts continue through the evening push, subsiding overnight. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/ KJFK TAF Comments: Tempo MVFR conditions might not occur. KLGA TAF Comments: Tempo MVFR conditions might not occur. KEWR TAF Comments: Tempo MVFR conditions might not occur. KTEB TAF Comments: Tempo MVFR conditions might not occur. KHPN TAF Comments: Tempo MVFR conditions might not occur. . KISP TAF Comments: Tempo MVFR conditions might not occur. .OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... .Saturday...VFR. .Saturday night...IFR. Snow at KSWF/KHPN. Rain-snow mix for KISP/KGON, and possibly KJFK/KLGA/KEWR/KTEB/KBDR as well. .Sunday...VFR. .Monday...CHC late day MVFR with -shra. -shra/MVFR/IFR at night. .Tuesday...MVFR or IFR early, otherwise VFR with SW wind G20KT possible. .Wednesday...Mainly VFR, chc -shra/MVFR. && .MARINE... A cold front moves across the waters this afternoon. Strong cold advection late this afternoon into this evening will result in SCA NW gusts on all waters. Prior to that time though, a SE swell on the ocean waters will increase seas to 5 ft on the ocean waters this morning, which eventually build to near 7 ft this evening. Winds and seas quickly come down overnight as high pressure builds across the waters. A light-moderate pressure gradient over the waters will limit winds to around 15 kt or less from Saturday night through Tuesday night, and likely keep gusts to 20 kt or less as well. Seas on the coastal ocean waters should be 4 ft or less through Monday, then could reach around 5 ft over mainly southern portions of the coastal ocean zones Monday night-Tuesday night due to a S swell along with persistent SW flow. && .HYDROLOGY... Rainfall through this afternoon will amount to less than a quarter of an inch. Around 1/3 to 2/3 of an inch of liquid equivalent is expected Saturday night. With most, if not all of this falling in the form of snow, no hydrologic impacts are expected. No significant hydrologic impacts are expected Sunday through the middle of next week. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from Saturday evening through Sunday morning for CTZ005>012. NY...Winter Storm Watch from Saturday evening through Sunday morning for NYZ069>075-078>081-176>179. NJ...Winter Storm Watch from Saturday evening through Sunday morning for NJZ002-004-006-103>108. MARINE...Small Craft Advisory from 6 PM this evening to 1 AM EST Saturday for ANZ330-335-338-340-345. Small Craft Advisory until 6 AM EST Saturday for ANZ350-353- 355. && $$ SYNOPSIS...Maloit/DW NEAR TERM...JM/DW SHORT TERM...DW LONG TERM...Maloit AVIATION...JC MARINE...Maloit/JM/DW HYDROLOGY...Maloit/DW EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.